U.S. patent number 4,932,439 [Application Number 07/398,345] was granted by the patent office on 1990-06-12 for solenoid actuated three-way valve.
This patent grant is currently assigned to Colt Industries Inc.. Invention is credited to Lawrence McAuliffe, Jr..
United States Patent |
4,932,439 |
McAuliffe, Jr. |
June 12, 1990 |
Solenoid actuated three-way valve
Abstract
A solenoid actuated three-way valve is formed with a central
passage communicating at one end with a vent passage via a first
valve seat and communicating at its opposite end with a pressure
supply port via a second valve seat. A control port directly
communicates with the central passage at all times. An armature is
slidable within the passsage to block one of the valve seats while
opening the other and is resiliently biased toward one seat by a
compression spring and magnetically biased toward the other seat by
energization of the solenoid coil. Flux washers at opposite ends of
the coil contact a ferromagnetic casing to provide an efficient
flux path enabling rapid response of the armature to coil
energization. One valve seat is loccated at one end of a pole piece
threadably adjustable within one of the flux washers to establish a
working gap in the magnetic circuit of a minimum width of the
valve. A relatively large return gap is provided to minimize
frictional losses within the valve.
Inventors: |
McAuliffe, Jr.; Lawrence (Ann
Arbor, MI) |
Assignee: |
Colt Industries Inc. (New York,
NY)
|
Family
ID: |
26961530 |
Appl.
No.: |
07/398,345 |
Filed: |
August 24, 1990 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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282587 |
Dec 12, 1988 |
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Current U.S.
Class: |
137/625.65;
251/129.18; 251/129.21 |
Current CPC
Class: |
F16K
31/0606 (20130101); F16K 31/0627 (20130101); Y10T
137/86622 (20150401) |
Current International
Class: |
F16K
31/06 (20060101); F15B 013/044 () |
Field of
Search: |
;137/625.65
;251/129.18,129.21 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Michalsky; Gerald A.
Attorney, Agent or Firm: Potoroka, Sr.; Walter
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION
This application is a continuation-in-part of my co-pending
application Ser. No. 07/282,587, filed Dec. 12, 1988, now
abandoned.
Claims
What is claimed is:
1. In a solenoid actuated three way valve intended for rapidly
repeated cyclic operation, said valve comprising an energizable
solenoid coil, an elongate armature mounted within a main passage
extending coaxially through said coil and having first and second
valve head means respectively located at its opposite ends, first
and second valve seat means at the respective opposite ends of said
main passage, said first and second seat means be spaced from each
other axially of said main passage by a distance greater than the
length of said armature, means defining first and second flow
passages opening into said main passage through the respective
first and second valve seats, spring means biassing said armature
in one direction to normally maintain said first valve head means
engaged with said first valve seat to block fluid communication
between said main passage and said first passage, said solenoid
coil being operable when energized to magnetically bias said
arpature in the opposite direction to engage said second valve head
means with said second valve seat to block fluid communication
between said main passage and said second passage, and means
defining a third flow passage opening into said main passage,
the improvement wherein said valve includes first and second
annular flux washers located at the respective opposite ends of
said coil, a hollow generally cylindrical metal outer housing
member externally surrounding said coil and contacting the outer
periphery of said first and second flux washers to define a low
reluctance magnetic flux path therebetween, said first valve seat
being located axially beyond that side of said first flux washer
remote from said coil, a pole piece mounted upon said second flux
washer and projecting from said second flux washer into said
passage beyond the adjacent end of said coil, said second valve
seat being located on said pole piece and said pole piece being
adjustable axially of said main passage to adjustably establish a
minimum working gap adequate to accomodate fluid flow between said
second valve seat and said second valve head means when said
solenoid coil is deenergized, said first flux washer having a
central bore therethrough coaxial of said main passage and of a
diameter falling within the range of 110% and 140% of the diameter
of said main passage.
2. The invention defined in claim 1 wherein said main passage is
defined at least in part by a central bore extending through a
solenoid coil supporting bobbin of non magnetic material, said
armature being of an outer diameter such that the armature is
slidably received within said central bore, with a minimum
clearance, the outer diameter of said armature being between 15 and
30% of the outer diameter of said coil.
3. The invention defined in claim 1 wherein the axial thickness of
said first flux washer is between 30 and 50 percent of the axial
length of said coil.
4. The invention defined in claim 1 wherein said armature is
slidably received within said main passage with a radial clearance
R.sub.1 from the wall of said main passage, and the radial
clearance R.sub.2 between said armature and said central bore of
said first flux washer is such that R.sub.1 /R.sub.2 is less than
0.2.
5. The invention defined in claim 4 wherein said armature includes
means defining fluid flow grooves in the outer surface of said
armature extending axially from one end of said armature to the
other.
6. The invention defined in claim 1 wherein said armature, flux
washers and outer housing member are of a material selected from
the group consisting of:
a. 2.5% silicon iron
b. 12L14
c. 0.45% to 0.9% phosphorus iron.
Description
BACKGROUND OF THE INVENTION
I. Field of the Invention
The present invention is directed to a solenoid actuated three-way
valve of the type employed in pulse width modulated pressure
control systems wherein the pressure at a control port of the valve
is regulated by cyclically connecting the control port alternately
to a high-pressure source and a low-pressure source to achieve a
pressure at the control port proportional to the percentage of time
during which the control port is connected to the high-pressure
port.
II. Description of the Related Art
Valves of the foregoing type are being increasingly employed to
control automotive transmission systems by regulating the
engagement pressure of various clutches within the transmission to
regulate the torque transmitted through the individual clutch. An
on-board microprocessor receives various inputs representative of
vehicle operating conditions, such as vehicle speed, engine RPM,
throttle setting, etc. The processor is programmed to compute the
optimum transmission ratio in accordance with the various inputs.
In response to the inputs, the processor generates a pulse width
modulated control signal at a constant frequency, typically in the
order of 60 Hz, which controls energization of the solenoids of the
various solenoid valves. During each cycle of the pulse width
modulated control signal, the coil of a solenoid actuated valve is
energized for a predetermined percentage of the cycle period and
deenergized for the remainder of the cycle. Over a series of
successive cycles, the pressure at the control port of the valve,
assuming the pressure at the low-pressure port is zero, will be a
percentage of the pressure at the high-pressure port equal to the
percentage of time the high-pressure port is connected to the
control port.
The requirements of a solenoid valve employed in such a system are
basically that shifting of the valve armature between its alternate
positions must closely and accurately track the rapidly repeated
energization and deenergization of the solenoid coil. This requires
the development of a maximum axial force applied to the solenoid
armature upon energization of the coil, and minimum parasitic
losses, such as friction, eddy currents, etc. within the
assembly.
The present invention is directed to a solenoid valve which
efficiently meets these last requirements, as well as the universal
requirement of the automotive industry of low unit cost and
simplified construction.
SUMMARY OF THE INVENTION
A solenoid valve embodying the present invention includes a
one-piece bobbin of a molded, non-magnetic material formed with a
central passage extending axially through the bobbin. At one end of
the bobbin, a pair of projecting posts are integrally formed to
serve as mounts for electrical connectors to be connected to the
opposite ends of the winding of the solenoid coil which is would
upon the bobbin. Annular flux washers are mounted on the bobbin
adjacent each end of the bobbin, one of the flux washers having a
pair of bores for passing the connector mounting posts on the
bobbin and a central threaded bore into which a pole piece is
adjustably threaded with the inner end of the pole piece blocking
one end if the central passage through the bobbin. The pole piece
is formed with an axial passage which extends from a valve seat at
the end disclosed within the central passage to a vent port opening
to atmosphere. The other flux washer is sandwiched between the
opposite end of the bobbin and a valve housing with its inner
periphery at a fairly substantial radial spacing outwardly from
their central passage. The valve housing has a chamber
communicating with the central passage in the bobbin. This chamber
is at all times in communication with a control port via a passage
in the valve housing. A supply port in the valve housing
communicates via a supply passage in the housing with a valve seat
opening into the chamber in coaxial alignment with the central
passage. An armature is slidably received within the central
passage between the two valve seats and is axially movable within
the passage between end limits defined by the engagement of the
armature with one or the other of the two valve seats. The armature
is grooved along its outer surface to provide a substantially
unrestricted flow passage between the opposite ends of the armature
while enabling the armature to slidably engage the central passage
wall to maintain the armature accurately centered within the
passage.
In a preferred form of the invention, a compression spring is
engaged between the pole piece and armature to bias the armature to
seal the valve port which communicates with the supply port, the
string bias exceeding the pressure exerted on the armature by
pressure at the supply port. In this arrangement, the control port
is thus normally in direct fluid communication with the vent port.
When the solenoid is energized, the armature is magnetically
shifted to unseat the armature from the valve seat connected to the
supply port and to simultaneously seal the valve port in
communication with the vent passage, the magnetic force of the
energized coil being augmented by the supply port pressure. In this
energized condition of the solenoid, the control port is connected
to the supply port.
The flux washers, bobbin and valve housing are held in assembled
relationship with each other by a sheet metal housing which axially
clamps the parts into assembled relationship with each other and
also serves as a portion of the path for the magnetic flux to
increase the efficiency of the magnetic shifting of the armature. A
relatively short axial air gap between the pole piece and armature
maximizes the magnetic shifting force which a relatively large
radial air gap between the opposite end of the armature and flux
washer minimizes friction producing radial forces on the
armature.
Other objects and features of the invention will become apparent by
reference to the following specification and to the drawing.
BRIEF DESCRIPTION OF THE DRAWING
The single figure of drawings shows a cross-sectional view, taken
on an axial plane, of a three-way solenoid actuated valve embodying
the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The valve shown in the drawing includes a solenoid bobbin
designated generally 10 which may be conveniently molded from any
of several suitable non-magnetic, thermoplastic materials. The
bobbin is formed with an annular recess 12 in which the solenoid
coil S is wound and the ends of the wire of the coil are led
through bores in the bobbin (not shown) to electrical connectors 14
fixedly mounted in a pair of axial projections 16 formed at one end
of the bobbin.
The bobbin is also formed with a central passage 18 which extends
axially entirely through the bobbin.
At the upper end of bobbin 10, an annular flux washer 20 of
ferromagnetic material is seated upon a shoulder 22 formed on
bobbin 10. Flux washer 20 is formed with a pair of bores 23 located
to loosely receive connector projections 16. A central bore 24
through washer 20 is coaxially aligned with central passage 18 of
the bobbin and is internally threaded to threadably receive a pole
piece 26 which is likewise formed of a ferromagnetic material.
The lower end of pole piece 26 projects into the upper end of
central passage 18 and is sealed to the inner wall of passage 18 as
by an O-ring 28 which will accommodate axial adjustment of the pole
piece relative to flux washer 20 for purposes referred to below. A
passage 30 extends axially through pole piece 26 to open at its
lower end into central passage 18 via an annular valve seat 32
formed on the lower end of the pole piece. In the particular
embodiment shown in the drawing, passage 30 opens at its upper end
to atmosphere and passage 30 constitutes a vent passage.
For reasons to be discussed below, pole piece 26 is threadably
adjustable in washer 20 axially of passage 18 to establish an
accurately determined working gap or axial spacing between the
upper end of the solenoid armature 62 and valve seat 32 when the
armature is in the position shown in the drawings.
A second flux washer 34 is mounted at the lower end of bobbin 10
and formed with a central bore 36 received upon a reduced diameter
axial extension 38 formed on the lower end of the bobbin. For
reasons to be discussed below, the internal diameter of bore 36 is
between 110% and 140% of the diameter of passage 18 in the
bobbin.
Underlying flux washer 34 is a valve housing designated generally
40. Housing 40 is formed with a central recess 42 extending
downwardly from its upper end which is dimensioned to slidably
receive the lower end of projection 38 of the bobbin A central bore
44 extends upwardly through housing 40 from a supply port 46
located at the lower end of housing 40. Passage 44 opens into
chamber 42 via a valve seat 48 located at the bottom of recess 42.
At diametrically opposite sides of passage 44, a pair of bores 50
extend downwardly through valve housing 40 from its upper end to
open through an undercut shoulder 52 on housing 40 through control
ports 54. Valve housing 40 is conformed to be axially inserted into
a manifold, not shown, and sealed to the manifold as by O-rings 56,
58.
Valve housing 40, bobbin 10 and flux washers 20 and 34 are fixedly
secured in the assembled relationship shown in the drawing by a
sheet metal casing 60 which firmly clamps these parts in axial,
face-to-face relationship with each other. Casing 60 is of a
ferromagnetic material and also functions as a part of the flux
path of the magnetic flux induced by energization of solenoid coil
S.
Within central passage 18, an armature 62 is slidably mounted for
axial movement within passage 18 between valve seats 32 and 48. For
reasons to be discussed below, the outer diameter of armature 62 is
such as to establishing a close, but freely sliding fit within
passage 18. The axial length of armature 62 is less than the
spacing between the two valve seats (as adjusted by threadably
positioning pole piece 26 in flux washer 20) so that when one of
the heads 64, 66 is seated, sealed engagement with its valve seat,
the other valve head is disengaged from its associated seat by a
distance sufficient to accommodate an adequate flow of fluid
between the head and seat. Axial grooves 68 in the outer surface of
armature 62 provide a substantially unrestricted flow path between
the opposite ends of the armature to equalize fluid pressure at
opposite ends of the armature.
Spring 70 resiliently biases the armature 62 downwardly as viewed
is the drawing to place valve head 66 in seated engagement upon
valve seat 48, there by blocking fluid communication between supply
port 46 and chamber 42. Control ports 64 are in fluid communication
at all times with the chamber 42 via bores 50. With armature 62 in
the position shown in the drawing, chamber 42 is in fluid
communication with vent passage 30 via valve seat 32 and grooves 68
in armature 62.
Electrical energization of solenoid coil S is operable to generate
a magnetic flux which magnetically biases armature 62 upwardly from
the position shown in the drawing until the valve head 64 at the
upper end of armature 62 contacts valve seat 32. With valve seat 32
closed by valve head 64, communication between vent passage 30 and
control ports 54 is blocked, but at the same time valve head 66 has
been lifted upwardly out of engagement with valve seat 48 so that
supply port 46 (connected to a source of air under pressure, not
shown) is in fluid communication with control port 54 via passage
44, valve seat 48 and bores 50.
The valve is especially intended for use in a system in which
solenoid coil S is cyclically energized and deenergized under the
control of a pulse width modulated control signal. In a general
application, where air is used as the pressure fluid, supply port
46 will be connected to a source of air under pressure and control
ports 54 will be connected to the actuating chamber of a
pneumatically actuated device, while passage 30 will be simply
vented to atmosphere. The pulse width modulated control signal
which controls energization of solenoid coil S cyclically energizes
and deenergizes the solenoid coil so that the period of time within
a given cycle during which coil S is energized is varied in
accordance with variations of the control signal derived from a
microprocessor. As explained above, the microprocessor will receive
inputs representing various operating parameters and generate a
control signal output in accordance with the processor program.
As explained above, when the solenoid is deenergized and the
armature 62 is in the position shown in the drawing, control ports
54 and any controlled device connected to it will be vented to
atmosphere via pores 50, chamber 42, grooves 68 in armature 62 and
vent passage 30. Pressure from the supply source at supply port 46
is isolated from control port 54 at this time because valve head 66
of the armature is seated upon valve seat 48.
Upon energization of solenoid coil S, armature 62 is magnetically
biased upwardly to disengage valve head 66 from valve seat 48,
thereby placing supply port 46 in communication with control port
54 to supply pressure from the pressure source to the control
device. Simultaneously, valve head 64 engages valve seat 32 to
isolate vent passage 30 from the control and supply ports 54,
46.
When armature 62 is rapidly and continually cycled between its two
positions, control port 54 is alternately connected to vent passage
30 and to supply port 46. When control port 54 is connected to the
supply port 46, the pressure at control port 54 will tend to
increase to approach the pressure of the source connected to supply
port 46, while when control port 54 is connected to vent via
passage 30, the pressure at control port 54 will tend to drop
toward zero or atmospheric pressure. By continuously applying
alternate on-off cycles, the pressure at port 54 will stabilize at
a pressure which is a percentage of the supply source pressure
equal to the percentage of time over the given time period during
which the solenoid coil was energized.
Typical operating frequencies of a pulse width modulating control
system are in the neighborhood of 60 Hz, which means that the
armature 62 must be capable of rapid movement between its alternate
positions. Movement of armature 62 to the normal (solenoid
deenergized) position shown in the drawing is essentially under the
control of spring 70 and presents no substantial design problems.
Movement of the armature to its upper position as viewed in the
drawings depends upon the magnetic flux developed by energization
of the solenoid, and in particular the axial flow of the magnetic
flux across what will be referred to as the working gap which is
the axially spacing between valve head 64 and the opposed valve
seat 32. The development of a maximum axially directed magnetic
force upon armature 62 for a given number of ampere turns of
solenoid coil S requires a consideration of several design
parameters.
In addition to acting as a return spring, spring 70 also functions
as a pressure relief setting in the event the pressure at supply
port 46 should, for some reason or other, increase above a desired
value.
In the valve configuration described above, the magnetic circuit or
flow path of magnetic flux induced by energization of solenoid S
has two "air gaps", one of which is the working gap referred to
above -- i.e. the axial spacing between valve head 64 at the top of
the armature and the opposed valve seat 32 on the pole piece. The
second "air gap" is that between the wall of bore 36 in the lower
flux washer 34 and the outer diameter of armature 62.
The flow of flux across the working gap between valve head 64 and
its associated valve seat 32 is directed axially of the coil and it
is the magnetic force developed across this gap which acts to shift
armature 62 upwardly against the action of spring 70 to seat valve
head 64 against seat 32. Because the magnetic force developed
across the working gap varies inversely with the square of the
distance across the gap, obviously rapid response of the valve
dictates this distance be as small as possible. The minimum
distance or working gap length is established by the minimum fluid
flow requirements of the valve -- in other words, there must be
enough space left between valve head 64 and valve seat 32 when in
the position shown in the drawing to accommodate adequate fluid
flow through the opened valve 64, 32. This spacing, due to
manufacturing tolerences and variations in material characteristics
is difficult to calculate, hence the threaded adjustment of pole
piece 26 permits the working gap to be adjusted after assembly.
Flow of flux across the return gap between the surface of bore 36
in the lower flux washer and the outer diameter of armature 62 is
essentially flow along paths extending radially of the longitudinal
axis of the armature. This radially directed flow of flux has
substantially no direct effect upon axial movement of armature 62
beyond the fact that the power required to generate the flow of
flux across the return gap is not available to assist in driving
the armature is axial movement. Thus, it is generally considered by
the prior art to be good design practice to make the return gap or
radial clearance between the armature and bore 36 as small as
possible to minimize the power loss within the magnetic circuit.
This reasoning, however, overlooks an important fact which has been
ignored in the prior art.
It is generally assumed that because the inner wall of bore 36 and
the outer surface of armature 62 are circular and coaxial with each
other, the magnetic forces induced by the flow of magnetic flux
radially across the return gap counterbalance each other and
inherently result in an equilibrium condition in which there is no
not force tending to move the armature in any radial direction.
While this assumption is theoretically correct, this theoretical
equilibrium of forces is based on an overly optimistic assumption
that the opposed bore and armature surfaces are precisely circular
and precisely coaxial with each other and that the magnetic field
is precisely symmetrical. In theory, such equilibrium is possible,
in practice it cannot be achieved in devices produced on a mass
production basis.
If this magnetic equilibrium is not achieved, a net force will be
applied biassing the armature in a direction radially of its axis
and this force will increase with the resultant movement of the
armature. The armature will move radially until it is prevented
from moving further by engagement with the wall of passage 18. This
will result in frictional forces between the armature and passage
wall which are generally proportional to the force which presses
the armature against the wall. Where the return gap is minimized in
accordance with conventional design practice, the forces urging the
armature against the passage wall will be relatively high, and the
resultant frictional forces can typically absorb 20% or more of the
power required to axially shift the armature by energization of the
solenoid coil. Power losses of this magnitude can equal or exceed
any gain achieved by minimizing the return gap.
Thus, in accordance with the present invention a relatively wide
return gap is employed by making the internal diameter of bore 36 a
diameter which is somewhere within the range of 110% to 140% of the
outside diameter of the armature which, desirably is made as
closely fitting as possible to the internal diameter of passage 18
as is compatible with a freely sliding fit.
The magnetic reluctance of the return gap, where the gap is
relatively large, as described above, may be reduced by increasing
the area of the return gap -- i.e. increasing the axial thickness
of flux washer 34. As a rough rule of thumb, for a fast responding
solenoid valve of the type under consideration the thickness of the
flux return washer 34 should be between 30 and 50 percent of the
axial length of solenoid coil S.
Because the unbalanced magnetic force across the return gap which
induces radial movement of the armature increases rapidly as the
armature moves in response to this force, the normal radial
clearance between the outer diameter of the armature and the wall
of passage 18 should be made as small as possible to minimize this
movement, while at the same time allowing the armature to slide
freely through the passage. The axial grooves 68 in the armature
enable a major portion of the armature surface to slidably contact
the passage wall, while at the same time providing an adequate flow
path for the working fluid to flow through passage 18 from one end
of the armature to the other.
The ratio of the mechanical radial clearance between the armature
and wall of passage 18 to the magnetic clearance (return gap)
between the outer wall of the armature and bore 36 in flux washer
34 has a substantial effect on the frictional forces discussed
above. The ratio of the mechanical clearance to the magnetic
clearance should be as low as possible and should not exceed
0.2.
Selection of the material from which the armature, flux washers
pole piece 26 and casing 60 are constructed depends on the
particular application of the valve, taking into account cost
considerations.
Where cost considerations are paramount, as is frequently the case
in automotive applications, the material having the standard
designation 12L14 (a medium carbon leaded steel) is a preferred
material. In addition to its low material cost, 12L14 is easily
machined, a consideration where parts of complex state, such as the
slotted armature 62 and upper flux washer 20, are involved.
However, most automotive applications require the valve to operate
at temperatures well below freezing where higher forces are
required to overcome the viscosity of a cold working fluid
controlled by the valve. For low temperature operation, a 2.5%
silicon iron is preferred; however, this material is more costly
than 12L14 and more difficult to machine.
Where parts of complex shape are employed, a powdered metal of
0.45% to 0.9% phosphorus iron alloy may be the preferred material
because it may be pressed and sintered to form parts of complex
shape at a relatively low manufacturing cost and has somewhat
better performance characteristics than 12L14.
While one embodiment of the invention has been described in detai1,
it will be apparent to those skilled in the art the disclosed
embodiment may be modified. Therefore, the foregoing description is
to be considered exemplary rather than limiting, and the true scope
of the invention is that defined in the following claims.
* * * * *